1. Field of the Invention
This invention relates broadly to the field of electromagnetic energy transmission devices. More particularly, the invention relates to radio frequency transducers or couplers. More specifically, the invention discloses a stripline to waveguide transition device, adapted for coupling microwave electromagnetic energy traveling through a stripline into the air cavity of a waveguide under specific boundary conditions within the waveguide.
2. Description of the Prior Art
Mixed microwave circuits, in which part of the circuit is in the form of conductively bounded hollow circular or rectangular guides (waveguides) and part is in the form of a conductor strip sandwiched by parallel dielectric slabs (stripline) are becoming increasingly popular with the development of microwave integrated circuit techniques. In such circuits, it is generally necessary to transition one or more times between transmission lines of these different types.
Printed circuit and thin film technology have made possible microwave integrated circuits in which many microwave functions are integrated into a single package using stripline as the sole transmission media throughout the package. However, some components are not susceptible to direct stripline connection and must be connected to hollow waveguides. A system which includes such components must therefore provide interconnections between stripline and waveguide transmission components. In many instances, it is convenient to join the waveguide and stripline in an end-to-end fashion especially where the system includes components which tend to be interconnected end-to-end. Such an end-to-end, coplanar, stripline-to-waveguide interconnection avoids structural fabrication problems and electrical energy losses encounted in orthogonal mating of such components as was customary in the prior art.
Coplaner structural interconnection of stripline and waveguide is relatively simple to achieve, but electrical coupling thereof presents difficulties. Typically, a transition must be provided between the principal TEM (Transverse Electro Magnetic) mode of the stripline and the dominant TE.sub.10 (Transverse Electric, one-zero) mode of a rectangular waveguide. As is well known in the art, such a transition may be accomplished by means of a probe inserted through the broad wall of the waveguide parallel to the electric field, i.e. perpendicular to the broad wall. Transition may also be accomplished by means of a loop inserted in a coplaner fashion in the end of a waveguide. The plane of the loop is normal to the magnetic field of the waveguide, and the loop is shorted to the wall of the guide. The former method utilizes electric field coupling, and is referred to as a top launch transition. The latter employs magnetic field coupling, and is referred to as an end launch transition. A top launch necessitates the perpendicular orientation of the TEM and TE.sub.10, stripline and waveguide, transmission lines and is not as convenient for use with microwave integrated circuitry as is end-to-end coupling.
Though stripline and rectangular waveguide possess structural similarities, they are physically distinct and hence possess different characteristic impedances. A means is therefore needed to provide a good impedance match for the end launch TEM to TE.sub.10 transition. Transducers now being used in the art for this purpose employ well-known impedance matching techniques such as dielectric matching, transition through an intermediary coaxial section, or tapering members in the transition region.
It is further necessary that the junction boundary conditions for electric and magnetic field be satisfied at the point where the stripline ends and the waveguide begins.
The invention disclosed herein provides a simple, effective and convenient means for providing a good impedance match between a stripline and a waveguide not disclosed in the prior art, while at the same time establishing requisite boundary conditions for a wave traveling down the waveguide.